JP2022077462A - Electrode, battery cell, cell stack, and redox flow battery system - Google Patents

Abstract

To provide an electrode which can easily achieve both of the improvement of a battery reaction performance and a long life.SOLUTION: An electrode comprises: a base material; and a catalyst carried by the base material. The catalyst contains: a first catalyst structured by a complex oxide of a first element and a second element. An element of each of the first element and the second element is different. The first element is one kind of elements, selected from a group of Ti, Sn, Ce, W, Ta, Mo, and Nb. The second element is one kind of elements, selected from a group of Nb, Mn, Fe, Cu, Ti, Sn, and Ce. A rate of the number of mols of the first element to a total number of mols of the first element and the second element in the complex oxide is 0.4 or larger and is less than 0.9.SELECTED DRAWING: Figure 3

Description

The present disclosure relates to electrodes, battery cells, cell stacks, and redox flow battery systems.

The electrode for a redox flow battery of Patent Document 1 includes a substrate and a catalyst portion supported on the substrate. The catalyst part is composed of an oxide of one kind of element. This catalyst section improves the battery reactivity of the redox flow battery system.

International Publication No. 2019/239732

In addition to improving battery reactivity, it is desired to extend the life of the electrode.

One of the purposes of the present disclosure is to provide an electrode that can easily achieve both improvement in battery reactivity and long life. One of the objects of the present disclosure is to provide a battery cell, cell stack, and redox flow battery system having excellent battery reactivity over a long period of time.

The electrodes according to the present disclosure are
An electrode comprising a base material and a catalyst supported on the base material.
The catalyst includes a first catalyst composed of a composite oxide of a first element and a second element.
The first element and the second element are different elements and are different from each other.
The first element is one element selected from the group consisting of Ti, Sn, Ce, W, Ta, Mo, and Nb.
The second element is one element selected from the group consisting of Nb, Mn, Fe, Cu, Ti, Sn, and Ce.
The ratio of the number of moles of the first element to the total number of moles of the first element and the second element in the composite oxide is 0.4 or more and less than 0.9.

The battery cell according to the present disclosure is
The electrode according to the present disclosure is provided.

The cell stack according to the present disclosure is
A plurality of battery cells according to the present disclosure are provided.

The redox flow battery system according to this disclosure is
It comprises an electrode according to the present disclosure, a battery cell according to the present disclosure, or a cell stack according to the present disclosure.

The electrodes according to the present disclosure can easily achieve both improvement in battery reactivity and long life.

The battery cell, cell stack, and redox flow battery system according to the present disclosure are excellent in battery reactivity over a long period of time.

FIG. 1 is a perspective view showing an outline of electrodes provided in the redox flow battery system according to the embodiment. FIG. 2 is an enlarged view showing an outline of the region surrounded by the alternate long and short dash line circle of the electrode shown in FIG. 1. FIG. 3 is a cross-sectional view showing an outline of a state in which an electrode is cut along the III-III cutting line of FIG. FIG. 4 is a cross-sectional view showing an outline of another example in which the electrode is cut along the III-III cutting line of FIG. FIG. 5 is a cross-sectional view showing an outline of still another example in which the electrode is cut along the III-III cutting line of FIG. FIG. 6 is an enlarged view showing an enlarged outline of another example of the region surrounded by the one-point chain circle of the electrode shown in FIG. 1. FIG. 7 is a cross-sectional view showing an outline of a state in which an electrode is cut along the VII-VII cutting line shown in FIG. FIG. 8 is a schematic configuration diagram of the redox flow battery system according to the embodiment. FIG. 9 is a schematic configuration diagram of a cell stack provided in the redox flow battery system according to the embodiment. FIG. 10 is a diagram showing a graph of analysis results when the catalyst is X-ray diffracted in Test Example 1. FIG. 11 is a diagram showing a graph of peak angles at a specific crystal plane of the catalyst in Test Example 1. FIG. 12 shows the sample No. of Test Example 2. From 2-1 sample No. It is a figure which shows the linear sweep voltammogram of 2-5. FIG. 13 shows the sample No. of Test Example 2. It is a figure which shows the linear sweep voltammogram of 2-6. FIG. 14 shows the sample No. of Test Example 2. 2-7 and sample No. It is a figure which shows the linear sweep voltammogram of 2-8. FIG. 15 shows the sample No. of Test Example 2. From 2-9, sample No. It is a figure which shows the linear sweep voltammogram of 2-11. FIG. 16 shows the sample No. of Test Example 2. 2-12 and sample No. It is a figure which shows the linear sweep voltammogram of 2-13.

<< Explanation of Embodiments of the present disclosure >>
First, embodiments of the present disclosure will be listed and described.

(1) The electrode according to one aspect of the present disclosure is
An electrode comprising a base material and a catalyst supported on the base material.
The catalyst includes a first catalyst composed of a composite oxide of a first element and a second element.
The first element and the second element are different elements and are different from each other.
The first element is one element selected from the group consisting of Ti, Sn, Ce, W, Ta, Mo, and Nb.
The second element is one element selected from the group consisting of Nb, Mn, Fe, Cu, Ti, Sn, and Ce.
The ratio of the number of moles of the first element to the total number of moles of the first element and the second element in the composite oxide is 0.4 or more and less than 0.9.

In the above form, it is easy to achieve both improvement of battery reactivity and extension of life. The reason is that it contains a first catalyst composed of a composite oxide containing the first element and the second element in a specific ratio. The first element has acid resistance and is difficult to dissolve in the electrolytic solution. The second element contributes to the improvement of battery reactivity.

(2) As one form of the above electrode,
The shape of the catalyst may be at least one shape selected from the group consisting of a spherical shape, an ellipsoidal shape, a scale shape, a needle shape, a polygonal columnar shape, a columnar shape, an elliptical columnar shape, a membrane shape, and a layered shape.

The catalyst having the above-mentioned shape is easily supported on the base material and also easily suppresses a decrease in the flowability of the electrolytic solution.

(3) As one form of the above electrode,
The material of the base material may include C or Ti.

The base material containing the above materials has excellent battery reactivity.

(4) As one form of the above electrode,
The base material is a fiber aggregate or a sintered body, and is
The fiber aggregate may be a non-woven fabric, a woven fabric, or a paper.

Since the fiber aggregate tends to increase the number of contacts between the fibers, it is easy to increase the conductivity. Since it is easy to secure voids in the base material of the fiber aggregate, it is easy to improve the flowability of the electrolytic solution. The sintered body is a sintered body obtained by compression molding a plurality of particles. Since the sintered body tends to have many contacts between particles, it is easy to increase the conductivity. Since it is easy to secure voids in the base material of the sintered body, it is easy to improve the flowability of the electrolytic solution.

(5) As one form of the above electrode,
It may be provided with a binder in which the catalyst is bonded to the substrate.

The above embodiment facilitates the construction of battery cells, cell stacks, and redox flow battery systems that are excellent in battery reactivity over a long period of time. The reason is that the catalyst is firmly supported on the base material by the binder, so that the catalyst does not easily fall off from the base material.

(6) As one form of the electrode of (5) above,
The binder may contain one or more selected from the group consisting of resins, metals, carbides, and metal oxides.

The above-mentioned form makes it easy to firmly fix the catalyst to the base material. Therefore, the above-mentioned form easily suppresses the catalyst from falling off from the substrate for a long period of time. In particular, even in the long-term operation of the redox flow battery system, the catalyst does not easily fall off from the base material.

(7) The battery cell according to one aspect of the present disclosure is
The electrode is provided with any one of the above (1) to (6).

The above form has excellent battery reactivity over a long period of time. The reason is that the battery cell is provided with an electrode that easily achieves both improvement in battery reactivity and long life.

(8) The cell stack according to one aspect of the present disclosure is
A plurality of the battery cells of (7) above are provided.

The above form has excellent battery reactivity over a long period of time. The reason is that the battery cell provided in the cell stack is provided with an electrode that easily achieves both improvement in battery reactivity and long life.

(9) The redox flow battery system according to one aspect of the present disclosure is
It includes any one of the electrodes (1) to (6), the battery cell of (7), or the cell stack of (8).

The above form has excellent battery reactivity over a long period of time. The reason is that the redox flow battery system includes an electrode that facilitates both improvement of battery reactivity and long life, a battery cell provided with the electrode, or a cell stack including the battery cell.

<< Details of Embodiments of the present disclosure >>
Details of the redox flow battery system according to the embodiment of the present disclosure will be described below. The same reference numerals in the figure indicate the same names. Hereinafter, the redox flow battery system may be referred to as an RF battery system.

<< Embodiment >>
[Redox flow battery system]
The RF battery system 1 of the embodiment will be described with reference to FIGS. 1 to 9. As shown in FIG. 8, the RF battery system 1 includes a battery cell 10 and a circulation mechanism for circulating an electrolytic solution in the battery cell 10. The battery cell 10 has a positive electrode 14, a negative electrode 15, and a diaphragm 11. The diaphragm 11 is arranged between the positive electrode 14 and the negative electrode 15. At least one of the positive electrode 14 and the negative electrode 15 is composed of the electrode 100 shown in FIG. The electrode 100 includes a catalyst 120 shown in FIG. 3 and the like. One of the features of the RF battery system 1 of the present embodiment is that the catalyst 120 includes a specific first catalyst 121. The following description will be given in the order of the outline and basic configuration of the RF battery system 1 and the details of each configuration of the RF battery system 1 of the present embodiment.

[Overview of RF battery system]
The RF battery system 1 charges and stores the electric power generated by the power generation unit 510, discharges the stored electric power, and supplies the stored electric power to the load 530 (FIG. 8). The RF battery system 1 is typically connected between the power generation unit 510 and the load 530 via the AC / DC converter 500 and the substation equipment 520. Examples of the power generation unit 510 include a solar power generation device, a wind power generation device, and other general power plants. Examples of the load 530 include electric power consumers. The RF battery system 1 uses a positive electrode electrolytic solution and a negative electrode electrolytic solution. The positive electrode electrolytic solution and the negative electrode electrolytic solution contain metal ions whose valences change due to redox as active materials. Charging and discharging of the RF battery system 1 is performed by utilizing the difference between the redox potential of the ions contained in the positive electrode electrolytic solution and the redox potential of the ions contained in the negative electrode electrolytic solution. In FIG. 8, the solid line arrow between the AC / DC converter 500 and the substation equipment 520 means charging, and the broken line arrow means discharging. The RF battery system 1 is used, for example, for load leveling applications, applications such as instantaneous low compensation and emergency power sources, and applications for smoothing the output of natural energy such as solar power generation and wind power generation, which are being introduced in large quantities. To.

[Basic configuration of RF battery]
The RF battery system 1 includes a battery cell 10 separated into a positive electrode cell and a negative electrode cell by a diaphragm 11 that allows hydrogen ions to permeate.

The positive electrode cell 14 is built in the positive electrode cell. The positive electrode electrolytic solution circulates in the positive electrode cell by the positive electrode circulation mechanism 10P. The positive electrode circulation mechanism 10P includes a positive electrode electrolyte tank 18, a supply pipe 20, a discharge pipe 22, and a pump 24. The positive electrode electrolyte tank 18 stores the positive electrode electrolyte. A positive electrode electrolytic solution flows through the supply pipe 20 and the discharge pipe 22. The supply pipe 20 connects the positive electrode electrolyte tank 18 and the positive electrode cell. The discharge pipe 22 connects the positive electrode cell and the positive electrode electrolyte tank 18. The pump 24 pumps the positive electrode electrolyte in the positive electrode electrolyte tank 18. The pump 24 is provided in the middle of the supply pipe 20.

The negative electrode cell 15 is built in the negative electrode cell. The negative electrode electrolytic solution is circulated in the negative electrode cell by the negative electrode circulation mechanism 10N. The negative electrode circulation mechanism 10N includes a negative electrode electrolyte tank 19, a supply pipe 21, a discharge pipe 23, and a pump 25. The negative electrode electrolyte tank 19 stores the negative electrode electrolyte. The negative electrode electrolytic solution flows through the supply pipe 21 and the discharge pipe 23. The supply pipe 21 connects the negative electrode electrolyte tank 19 and the negative electrode cell. The discharge pipe 23 connects the negative electrode cell and the negative electrode electrolyte tank 19. The pump 25 pumps the negative electrode electrolytic solution in the negative electrode electrolytic solution tank 19. The pump 25 is provided in the middle of the supply pipe 21.

During the charging / discharging operation, the positive electrode electrolytic solution and the negative electrode electrolytic solution are circulated from the positive electrode electrolytic solution tank 18 and the negative electrode electrolytic solution tank 19 through the supply pipe 20 and the supply pipe 21 by the pump 24 and the pump 25 to flow the positive electrode cell and the negative electrode. It is supplied to the cell. The positive electrode electrolytic solution and the negative electrode electrolytic solution flow from the positive electrode cell and the negative electrode cell through the discharge pipe 22 and the discharge pipe 23, and are discharged to the positive electrode electrolyte tank 18 and the negative electrode electrolyte tank 19. By this supply and discharge, the positive electrode electrolytic solution and the negative electrode electrolytic solution are circulated in the positive electrode cell and the negative electrode cell. The pump 24 and the pump 25 are stopped during standby without charging / discharging. That is, the positive electrode electrolyte and the negative electrode electrolyte are not circulated.

[electrode]
As described above, the electrode 100 of the present embodiment shown in FIG. 1 constitutes at least one of the positive electrode 14 and the negative electrode 15. The electrode 100 has a base material 110 shown in FIG. 2 and the like, and a catalyst 120 shown in FIG. 3 and the like.

(Base material)
The base material 110 contributes to the battery reaction. The base material 110 holds the catalyst 120.

<Material>
The material of the base material 110 is not particularly limited as long as it has conductivity. The material of the base material 110 includes C (carbon) or Ti (titanium). Since the base material 110 contains C or Ti, it is easy to construct the electrode 100 having excellent battery reactivity. The base material 110 may be composed of the above-mentioned single element or may be composed of a compound containing the above-mentioned element. Examples of the compound include carbides, carbonitrides and Ti oxides. The base material 110 may contain elements other than the above-mentioned materials. For example, the base material 110 is composed of a group consisting of Ru (ruthenium), Ir (iridium), W (tungsten), Pt (platinum), Au (gold), Pd (palladium), Mn (manganese), and a conductive polymer. It may contain one selected material. The material of the base material 110 is obtained by X-ray diffraction.

The base material 110 is made of a porous material. Specific examples of the porous material include either the fiber aggregate 111 shown in FIG. 2 or the sintered body 112 shown in FIG. The fiber aggregate 111 is mainly composed of a plurality of fibers 111a, and one selected from the group consisting of non-woven fabric, woven fabric, and paper can be mentioned. The non-woven fabric is made by entwining independent fibers. The woven cloth is made by weaving the warp and weft of fibers alternately. The paper has a plurality of fibers and a binder for binding the fibers. As the material of the binder of the paper, for example, as described later, the same material as the binder for binding the catalyst 120 to the base material 110 can be mentioned. Examples of the sintered body 112 include a sintered body obtained by compression molding a plurality of particles 112a. The fiber aggregate 111 is excellent in conductivity because it is easy to increase the number of contacts between the fibers 111a. The fiber aggregate 111 is excellent in the flowability of the electrolytic solution because it is easy to secure voids in the base material 110. The sintered body 112 is excellent in conductivity because it is easy to increase the number of contacts between the particles 112a. Since the sintered body 112 can easily secure voids in the base material 110, the sintered body 112 is excellent in the flowability of the electrolytic solution.

The average diameter of the cross section of the fiber 111a is, for example, 3 μm or more and 100 μm or less. When the average diameter of the fibers 111a is 3 μm or more, the strength of the fiber aggregate 111 is increased. When the average diameter of the fibers 111a is 100 μm or less, the surface area of the fibers 111a per unit weight becomes large, so that the base material 110 can carry out a sufficient battery reaction. Further, the average diameter of the fiber 111a is 5 μm or more and 50 μm or less, and particularly 7 μm or more and 20 μm or less. The average diameter of the cross section of the fiber 111a is the average diameter of a circle having an area equal to the area of the cross section of the fiber 111a, and is obtained as follows. The electrode 100 is cut to expose the cross section of the fiber 111a. Take at least 5 fields of view under a microscope. For three or more fibers 111a per field of view, the diameter of a circle having the same area as the cross-sectional area is obtained. Average the diameters of the circles obtained in the entire field of view.

The average particle size of the particles 112a is, for example, 3 μm or more and 500 μm or less. Since the average particle size of the particles 112a is 3 μm or more, the particles 112a can be easily handled at the manufacturing stage of the electrode 100. When the average particle size of the particles 112a is 500 μm or less, the surface area of the particles 112a per unit weight is large, and the base material 110 can carry out a sufficient battery reaction. The average particle size of the particles 112a is further 10 μm or more and 300 μm or less, and particularly 50 μm or more and 200 μm or less. The average particle size of the particles 112a is determined as follows. Take 5 or more observation fields under a scanning electron microscope. The length of the long axis of the ellipse in the three or more particles 112a is obtained for one observation field. Average the length of the long axis of the ellipse obtained in the entire observation field.

(catalyst)
The catalyst 120 promotes the battery reaction. The catalyst 120 includes a first catalyst 121. The first catalyst 121 is composed of a composite oxide of a first element and a second element. That is, the first catalyst 121 is a binary oxide. All of the catalyst 120 may be composed of the first catalyst 121. The catalyst 120 may include a second catalyst in addition to the first catalyst 121. Unlike the first catalyst 121, the second catalyst may be composed of, for example, an oxide of a single element. The illustration of the second catalyst is omitted. In the following description, a single element oxide may be referred to as a single oxide.

<Composition of composite oxide>
The first element and the second element in the composite oxide are different elements from each other. The first element is one element selected from the group consisting of Ti, Sn, Ce, W, Ta, Mo, and Nb. The second element is one element selected from the group consisting of Nb, Mn, Fe, Cu, Ti, Sn, and Ce. The first element has acid resistance and is difficult to dissolve in the electrolytic solution. The first element can be present in the electrolytic solution for a long period of time. The second element contributes to the improvement of battery reactivity.

The ratio of the number of moles of the first element to the total number of moles of the first element and the second element in the composite oxide satisfies 0.4 or more and less than 0.9. The ratio of the number of moles of the second element to the total number of moles of the first element and the second element in the composite oxide satisfies more than 0.1 and 0.6 or less. The total of the ratio of the number of moles of the first element and the ratio of the number of moles of the second element is 1.0. In the composite oxide, the electrode 100 is easy to achieve both improvement of battery reactivity and long life by satisfying the above-mentioned specific range between the ratio of the number of moles of the first element and the ratio of the number of moles of the second element. Can be built. The ratio of the number of moles of the first element is further 0.5 or more and 0.8 or less, and particularly 0.6 or more and 0.8 or less. That is, the ratio of the number of moles of the second element is further 0.2 or more and 0.5 or less, and particularly 0.2 or more and 0.4 or less.

For example, when the first element is Ti or Ce, the ratio of the number of moles of the first element may be 0.4 or more. That is, the ratio of the number of moles of the second element is 0.6 or less.

For example, when the first element is Sn, the ratio of the number of moles of the first element is 0.4 or more, more preferably 0.6 or more, and particularly 0.7 or more. That is, the ratio of the number of moles of the second element is 0.6 or less, 0.4 or less, and 0.3 or less.

For example, when the first element is W, Mo, or Nb, the ratio of the number of moles of the first element is 0.6 or more, further 0.7 or more. That is, the ratio of the number of moles of the second element is 0.4 or less, more preferably 0.3 or less.

In the following description, the elements and numbers described before the "colon (:)" indicate the type of the first element and the ratio of the number of moles of the first element. The elements and numbers described after the "colon (:)" indicate the type of the second element and the ratio of the number of moles of the second element.
Examples of Ti: Ce include 0.4 or more and 0.6 or less: 0.4 or more and 0.6 or less.
Examples of Ti: Mn, Ti: Sn, and Ti: Nb are 0.4 or more and 0.8 or less: 0.2 or more and 0.6 or less.
Sn: Mn may be 0.6 or more and 0.8 or less: 0.2 or more and 0.4 or less.
Examples of Sn: Cu are 0.7 or more and 0.8 or less: 0.2 or more and 0.3 or less.
Examples of Sn: Nb and Sn: Ce are 0.4 or more and 0.8 or less: 0.2 or more and 0.6 or less.
Further, Sn: Nb is 0.6 or more and 0.8 or less: 0.2 or more and 4.0.
Examples of Ce: Ti, Ce: Nb, and Ce: Mn include 0.4 or more and 0.8 or less: 0.2 or more and 0.6 or less.
Examples of W: Fe and W: Cu include 0.6 or more and 0.8 or less: 0.2 or more and 0.4 or less.
Mo: Fe may be 0.7 or more and 0.8 or less: 0.2 or more and 0.3 or less.
Examples of Nb: Ti include 0.6 or more and 0.8 or less: 0.2 or more and 0.4 or less.
Examples of Nb: Fe are 0.7 or more and 0.8 or less: 0.2 or more and 0.3 or less.

The combination of the first element and the second element can be further made into the following combinations.
The first element is one element selected from the group consisting of Ti, Sn, Ce, W, Ta, and Mo. The second element is one element selected from the group consisting of Nb, Mn, Fe, and Cu.

<Composition of single oxide>
Examples of the catalyst composed of a single oxide include known catalysts. The single element in the single oxide may be, for example, the above-mentioned first element or the above-mentioned second element, or may be an element different from the first element and the second element. Examples of the single oxide composed of the first element and the element different from the second element include IrO ₂ and RuO ₂ .

The composition of the catalyst 120 is determined by X-ray diffraction using the same apparatus as the substrate 110.

<shape>
The shape of the catalyst 120 may be at least one shape selected from the group consisting of a spherical shape, an ellipsoidal shape, a scaly shape, a needle shape, a polygonal columnar shape, a columnar shape, an elliptical columnar shape, a film shape, and a layered shape. Since the catalyst 120 has the above shape, it is easily supported on the base material 110 and the flowability of the electrolytic solution is unlikely to decrease. The ellipsoidal shape includes a long spherical shape and an oblate spherical shape. "Spherical", "elliptical", "scaly", "needle", "polygonal column", "cylindrical", and "elliptical column" are geometric spheres, ellipsoids, scales, needles. Includes not only polygonal columns, cylinders, and ellipsoidal columns, but also ranges that are considered to be substantially spheres, ellipsoids, scales, needles, polygonal columns, cylinders, and elliptical columns. For example, the "polygonal column" includes a shape having rounded corners.

<size>
The average particle size of the catalyst 120 is, for example, 1 nm or more and 100 μm or less. The catalyst 120 having a size of 1 nm or more is easily held by the base material 110. A catalyst 120 having a size of 100 μm or less tends to improve battery reactivity. The average particle size of the catalyst 120 is further 5 nm or more and 10 μm or less, and particularly 10 nm or more and 1 μm or less. The flat grain size of the catalyst 120 is the average of the diameters of circles having an area equal to the area of the cross section of the catalyst 120, and is obtained as follows. The electrode 100 is cut to expose the cross section of the catalyst 120. Take five or more observation fields under a scanning electron microscope. The diameter of a circle having the same area as the cross-sectional area of three or more catalysts 120 is obtained for one observation field. Average the diameters of the circles obtained in the entire observation field. The average particle size of only the first catalyst 121 may be 1 nm or more and 100 μm or less.

<Existence ratio>
The abundance ratio of the catalyst 120 in the electrode 100 is, for example, 0.1% by mass or more and 70% by mass or less. The abundance ratio of the catalyst 120 is the mass ratio of the total content of the elements constituting the catalyst 120 when the electrode 100 is 100% by mass. For example, when the electrode 100 is composed of the base material 110 and the catalyst 120 as shown in FIG. 3 or FIG. 4, the total content of the base material 110 and the catalyst 120 is 100% by mass. When the electrode 100 is composed of the base material 110, the catalyst 120, and the binder 130 as shown in FIG. 5, the total content of the base material 110, the catalyst 120, and the binder 130 is 100% by mass.

When the abundance ratio of the catalyst 120 is 0.1% by mass or more and 70% by mass or less, the electrode 100 includes the catalyst 120 and the base material 110 can be secured. The abundance ratio of the catalyst 120 further includes 1% by mass or more and 70% by mass or less, and particularly 10% by mass or more and 50% by mass or less and 10% by mass or more and 30% by mass or less. The abundance ratio of the catalyst 120 is determined by thermogravimetric analysis.

The abundance ratio of the first catalyst 121 in the catalyst 120 is, for example, 30% by mass or more. The abundance ratio of the first catalyst 121 is the ratio of the total mass of the first catalyst 121 when the entire catalyst 120 is 100% by mass. When the abundance ratio of the first catalyst 121 is 30% by mass or more, it is easy to achieve both improvement of battery reactivity and extension of life. The abundance ratio of the first catalyst 121 is further 40% by mass or more, and particularly 50% by mass or more. The upper limit of the abundance ratio of the first catalyst 121 is 100% by mass. That is, the abundance ratio of the first catalyst 121 is 30% by mass or more and 100% by mass or less, further 40% by mass or more and 100% by mass or less, and particularly 50% by mass or more and 100% by mass or less.

<Existence form>
The catalyst 120 is supported on the base material 110. The term "supporting" as used herein means that the catalyst 120 is fixed in a state of being conductive on the base material 110. As the form in which the catalyst 120 is fixed to the base material 110, there are a form in which the catalyst 120 is directly fixed to the base material 110 and a form in which the catalyst 120 is indirectly fixed to the base material 110.

As a form to be directly fixed, as shown in FIG. 3 or FIG. 7, a form in which the catalyst 120 adheres to the surface of the base material 110, and as shown in FIG. 4, at least a part of the catalyst 120 is embedded in the base material 110. The form is mentioned. Substantially all of the catalyst 120 may be embedded in the substrate 110. FIG. 7 shows a form in which all the catalysts 120 adhere to the surface of the base material 110 for convenience of explanation, but even when the base material 110 has particles 112a, at least a part of the catalyst 120 is particles. It may be buried in 112a.

The catalyst 120 has a portion exposed from the base material 110 and a portion buried in the base material 110 when a part of the catalyst 120 is embedded in the base material 110. Since the catalyst 120 has a portion exposed from the base material 110, the catalyst 120 can exert a catalytic action from the initial stage of use of the electrode 100. Since the catalyst 120 has a portion embedded in the base material 110, the catalyst 120 is firmly supported on the base material 110. Therefore, it is easy to prevent the catalyst 120 from falling off from the base material 110 for a long period of time. In particular, the catalyst 120 is unlikely to fall off from the base material 110 even in the long-term operation of the RF battery system 1. When substantially all of the catalyst 120 is filled, the catalyst 120 is exposed when the electrode 100 deteriorates over time. The exposed catalyst 120 exerts a catalytic action.

As an indirectly fixed form, the catalyst 120 is not attached to the base material 110, and as shown in FIG. 5, the catalyst 120 is bound to the base material 110 by a binder 130 described later.

The catalyst 120 attached to the surface of the base material 110 (FIG. 3), the catalyst 120 partially embedded in the base material 110 (FIG. 4), and the catalyst 120 fixed by the binder 130 (FIG. 5). At least one catalyst 120 selected from the group consisting of the above, and the catalyst 120 (FIG. 4) completely embedded in the base material 110 may be mixed. The catalyst 120 completely buried in the base material 110 cannot exert a catalytic action at the initial stage of use of the electrode 100. Therefore, the catalyst 120 having a portion exposed from the base material 110 is always included.

<binder>
The electrode 100 may include a binder 130 as shown in FIG. The binder 130 binds the catalyst 120 to the substrate 110. The binder 130 firmly fixes the catalyst 120 in contact with the base material 110. Therefore, the catalyst 120 is unlikely to fall off from the base material 110 for a long period of time. The binder 130 covers at least a part of the catalyst 120. The binder 130 may be provided so as to cover the base material 110 and the catalyst 120 from the base material 110 to the catalyst 120.

Examples of the material of the binder 130 include a material that is difficult to dissolve in the electrolytic solution. The binder 130 contains one or more selected from the group consisting of resins, metals, carbides, and metal oxides. When the binder 130 contains these materials, the catalyst 120 is easily firmly fixed to the base material 110. Therefore, the catalyst 120 is unlikely to fall off from the base material 110 for a long period of time. In particular, even in the long-term operation of the RF battery system 1, the catalyst 120 is unlikely to fall off from the base material 110. Examples of the resin include phenol, polytetrafluoroethylene, and polyvinylidene fluoride. Examples of the metal include Ti and W. Examples of the carbide include titanium carbide, manganese carbide, and tungsten carbide. The metal oxide is an oxide different from the composite oxide constituting the first catalyst 121 and the single oxide constituting the second catalyst. Examples of the metal oxide include alumina and tin oxide. When the metal oxide is composed of tin oxide, the second catalyst is composed of a single oxide other than tin oxide.

The abundance ratio of the binder 130 in the electrode 100 is 1% by mass or more and 50% by mass or less, and further 20% by mass or more and 40% by mass or less. The abundance ratio of the binder 130 is the mass ratio of the total content of the elements constituting the binder 130 when the total content of the base material 110, the catalyst 120 and the binder 130 is 100% by mass. The mass ratio of the binder 130 is determined by thermogravimetric analysis.

(Porosity)
The porosity _P0 of the electrode 100 in the uncompressed state is, for example, 40% or more and 95% or less. The uncompressed state refers to a state before assembling the sub-stack 200s described later with reference to the battery cell 10 or the lower figure of FIG. The electrode 100 in the uncompressed state has a large number of pores because it has a porosity _P0 of 40% or more. Even if such an electrode 100 is compressed, pores are secured. Therefore, the electrode 100 in the compressed state is excellent in the flowability of the electrolytic solution. The electrode 100 in the uncompressed state has a porosity _P0 of 95% or less, so that the number of pores is not too large. When such an electrode 100 is compressed, the fibers tend to come into contact with each other. Therefore, the compressed electrode 100 is excellent in conductivity. Therefore, the electrode 100 having a porosity P0 of 95% or less in the uncompressed state makes it easy to construct an RF battery system ₁ having excellent battery reactivity. The porosity _P0 of the electrode 100 in the uncompressed state is further 50% or more and 95% or less, and particularly 60% or more and 85% or less. The porosity _P0 of the electrode 100 in the uncompressed state is obtained by the mercury intrusion method.

The porosity P1 of the compressed electrode ₁₀₀ is, for example, 30% or more and 90% or less. The compressed state means a state after assembling the battery cell 10 or the sub-stack 200s. The electrode 100 having a porosity P ₁ of 30% or more is excellent in the flowability of the electrolytic solution. The electrode 100 having a porosity P ₁ of 90% or less is excellent in conductivity. The porosity P ₁ of the compressed electrode 100 is further 40% or more and 80% or less, and particularly 45% or more and 70% or less. The porosity P ₁ of the compressed electrode 100 is obtained by P ₁ = 100-{(100-P ₀ ) d ₀ / d ₁ }. d ₀ is the thickness of the electrode 100 in the uncompressed state. d ₁ is the thickness of the compressed electrode 100. The thickness d ₁ of the electrode 100 in the compressed state is obtained by a compression test. The thickness d ₀ and the thickness d ₁ are the average values of the thicknesses of five or more places.

(Thickness)
The thickness _d0 of the electrode 100 in the uncompressed state is, for example, 0.20 mm or more and 1.00 mm or less. Even if the electrode 100 having a thickness d ₀ of 0.20 mm or more is compressed, the reaction field in which the battery reaction is performed can be increased. The electrode 100 in the uncompressed state has a thickness d ₀ of 1.0 mm or less, so that the electrode 100 is not excessively thick. Therefore, the electrode 100 having a thickness d ₀ of 1.0 mm or less can construct a thin RF battery system 1. The thickness _d0 of the electrode 100 in the uncompressed state further includes 0.3 mm or more and 1.00 mm or less, and particularly 0.40 mm or more and 0.70 mm or less.

The thickness d ₁ of the compressed electrode 100 may be, for example, 0.20 mm or more and 0.60 mm or less. The electrode 100 having a thickness d ₁ of 0.20 mm or more can increase the reaction field in which the battery reaction is performed. The electrode 100 having a thickness d ₁ of 0.60 mm or less can make the RF battery system 1 thin.

(Manufacturing)
The electrode 100 can be manufactured from step S1 to step S3.
In step S1, the material of the base material 110 and the coating liquid containing the constituent elements of the catalyst 120 are prepared.
In step S2, the coating liquid is applied to the surface of the material.
In step S3, the material to which the coating liquid is applied is heat-treated.

<Process S1>
Examples of the material to be prepared include the above-mentioned fiber aggregate or sintered body. The size and shape of the material may be appropriately selected so as to be the size and shape of the base material 110 in the desired electrode 100. The material used is one that has undergone at least one of surface area expansion and surface roughening by performing known blasting or etching treatment, or after blasting or etching treatment, selective etching of the known surface is performed to purify and activate the material. You may use the one that has undergone at least one of the etchings.

The coating liquid to be prepared contains a raw material and a solvent. Examples of the raw material include a first salt containing a first element and a second salt containing a second element constituting the catalyst 120. The ratio of the first salt to the second salt contained in the coating liquid is such that the ratio of the number of moles of the first element and the second element in the composite oxide constituting the catalyst 120 is within the above range after the step S3 described later. Adjust to meet. As the solvent, water or an organic solvent can be used. Examples of the organic solvent include ethanol and the like.

<Process S2>
Examples of the method of applying the coating liquid to the surface of the material include known methods such as a brush coating method, a spraying method, a dipping method, a flow coating method, and a roll coating method. After applying the coating liquid to the material, it dries.

<Process S3>
The conditions for heat treatment applied to the material to which the coating liquid is applied include the following conditions of atmosphere, temperature, and time. The atmosphere contains oxygen. The atmosphere containing oxygen includes an oxidizing atmosphere and an atmosphere in which the oxidation state is adjusted in a gas containing a reducing gas. The atmosphere may be, for example, an atmospheric atmosphere. The heat treatment temperature is, for example, 300 ° C. or higher and 700 ° C. or lower. The heat treatment time may be, for example, 10 minutes or more and 5 hours or less. By setting the heat treatment temperature to 300 ° C. or higher and the heat treatment time to 10 minutes or longer, the electrode 100 to which the catalyst 120 is attached can be manufactured by uniformly dispersing over the entire region of the base material 110. By setting the heat treatment temperature to 700 ° C. or lower and the heat treatment time to 5 hours or less, it is possible to prevent the abundance ratio of the catalyst 120 to the base material 110 from becoming too large. Further, the heat treatment temperature may be 400 ° C. or higher and 600 ° C. or lower, and particularly 450 ° C. or higher and 550 ° C. or lower. The heat treatment time may be further 15 minutes or more and 2 hours or less, and particularly 30 minutes or more and 1 hour or less.

By the above heat treatment, the constituent elements of the catalyst 120 permeate the inside of the base material 110 by thermal diffusion, and the catalyst 120 is dispersed and adhered to the surface of the base material 110. In the electrode 100 obtained by applying the coating liquid to the surface of the material and then heat-treating it, the catalyst 120 is mainly attached to the surface of the base material 110. Further, in the electrode 100 obtained by performing the above heat treatment, a part of the catalyst 120 may be buried in the base material 110.

If a coating liquid to which a raw material of an element constituting the binder 130 is further added is used as the above-mentioned coating liquid, an electrode 100 in which the catalyst 120 is fixed to the base material 110 by the binder 130 is manufactured. When the coating liquid containing the raw materials of the elements constituting the binder 130 is used, the steps S2 and S3 are the same as the above-mentioned steps S2 and S3 except that the heat treatment time is 15 minutes or more and 2 hours or less. be.

[Cell stack]
The battery cell 10 is usually formed inside a structure called a cell stack 200, as shown in FIGS. 8 and 9 below. The cell stack 200 includes a sub-stack 200s, two end plates 220, and a tightening mechanism 230. In the lower figure of FIG. 9, the cell stack 200 exemplifies a form including a plurality of sub-stacks 200s. As shown in the lower figure of FIG. 9, each sub-stack 200s includes a laminated body and two supply / discharge plates 210. As shown in FIGS. 8 and 9, the laminate is composed of a plurality of cell frames 16, a positive electrode 14, a diaphragm 11, and a negative electrode 15 laminated in this order. As shown in the lower figure of FIG. 9, the supply / discharge plate 210 is arranged at both ends of the laminated body. The two end plates 220 sandwich the plurality of sub-stacks 200s from the outside of the sub-stacks 200s at both ends. The tightening mechanism 230 tightens both end plates 220.

[Cell frame]
The cell frame 16 includes a bipolar plate 161 and a frame body 162 that surrounds the outer peripheral edge portion of the bipolar plate 161. The cell frame 16 forms a recess 160 in which the positive electrode 14 or the negative electrode 15 is arranged on the surface of the bipolar plate 161 and the inner peripheral surface of the frame 162. One battery cell 10 is formed between the bipolar plates 161 of the adjacent cell frames 16. A positive electrode cell and a negative electrode electrode 15 of adjacent battery cells 10 are formed on the front and back sides of the bipolar plate 161. A recess may be formed on the surface of the bipolar plate 161 to facilitate the flow of the electrolytic solution. The shape of this recess can be appropriately selected. The recess may have, for example, a plurality of grooves. For example, the plurality of grooves may be arranged at predetermined intervals in a direction orthogonal to the flow direction of the electrolytic solution. In this form, each groove extends linearly along the flow direction of the electrolytic solution.

The cell frame 16 includes an intermediate cell frame arranged between the adjacent battery cells 10 of the laminated body and end cell frames arranged at both ends of the laminated body. In the intermediate cell frame, the positive electrode 14 of one battery cell 10 is in contact with one surface of the bipolar plate 161 and the negative electrode 15 of the other battery cell 10 is in contact with the other surface of the bipolar plate 161. The end cell frame is in contact with one of the positive electrode 14 and the negative electrode 15 of the battery cell 10 on one surface of the bipolar plate 161 and has no electrode on the other surface of the bipolar plate 161. The configuration of the cell frame 16 is the same for both the intermediate cell frame and the end cell frame.

The frame body 162 supports the bipolar plate 161 and forms a region to be the battery cell 10 inside. The shape of the frame body 162 of this embodiment is a rectangular frame shape. That is, the opening shape of the recess 160 is rectangular. The frame 162 includes a liquid supply side piece and a liquid discharge side piece facing the liquid supply side piece. When the cell frame 16 is viewed in a plan view, if the direction in which the liquid supply side piece and the liquid drain side piece face each other is the vertical direction and the direction orthogonal to the vertical direction is the horizontal direction, the liquid supply side piece is on the lower side in the vertical direction. The drainage side piece is located on the upper side in the vertical direction. The liquid supply side piece has a liquid supply manifold 163, 164 and a liquid supply slit 163s, 164s for supplying an electrolytic solution inside the battery cell 10. The drain side piece has a drain manifold 165, 166, and drain slits 165s, 166s for draining the electrolytic solution to the outside of the battery cell 10. The flow of the electrolytic solution is from the lower side in the vertical direction to the upper side in the vertical direction of the frame body 162.

A liquid supply rectifying portion may be formed on the inner edge of the liquid supply side piece. The liquid supply rectifying unit diffuses the electrolytic solution supplied from the liquid supply slits 163s and 164s along the inner edge of the liquid supply side piece. A drainage rectifying portion may be formed on the inner edge of the drainage side piece. The effluent rectifying unit collects the electrolytic solution that has passed through the positive electrode 14 or the negative electrode 15 along the inner edge of the effluent side piece and circulates the electrolytic solution through the effluent slits 165s and 166s. The illustration of the liquid supply rectifying unit and the drainage rectifying unit is omitted.

The flow of each electrode electrolyte in the cell frame 16 is as follows. The positive electrode electrolytic solution flows from the liquid supply manifold 163 through the liquid supply slit 163s formed in the liquid supply side piece on one side of the frame body 162 and is supplied to the positive electrode electrode 14. Then, as shown by the arrow in the upper figure of FIG. 9, the positive electrode electrolytic solution flows from the lower side to the upper side of the positive electrode electrode 14 and flows through the drainage slit 165s formed in the drainage side piece to flow through the drainage manifold. It is discharged to 165. The supply and discharge of the negative electrode electrolytic solution is the same as that of the positive electrode electrolytic solution except that the negative electrode electrolytic solution is supplied and discharged on the other surface side of the frame body 162.

An annular seal member 167 such as an O-ring or a flat packing is arranged in an annular seal groove between the frames 162. The seal member 167 suppresses leakage of the electrolytic solution from the battery cell 10.

[Electrolytic solution]
The positive electrode electrolytic solution and the negative electrode electrolytic solution are circulated and supplied to the positive electrode electrode 14 and the negative electrode electrode 15 by the above-mentioned positive electrode circulation mechanism 10P and negative electrode circulation mechanism 10N. By this circulation, charging and discharging are performed with the reaction of changing the valence of ions, which are active materials contained in the positive electrode electrolytic solution and the negative electrode electrolytic solution. In the RF battery system 1, the positive electrode 14 is oxidatively deteriorated due to a side reaction accompanying charging and discharging, which tends to cause an increase in cell resistance. Therefore, if the electrode 100 is used for the positive electrode 14, the cell resistance can be effectively reduced.

The active material of the positive electrode electrolyte may contain one or more selected from the group consisting of manganese ion, vanadium ion, iron ion, polyic acid, quinone derivative, and amine. The active material of the negative electrode electrolytic solution may contain one or more selected from the group consisting of titanium ion, vanadium ion, chromium ion, polyic acid, quinone derivative, and amine. In FIG. 8, manganese (Mn) ions are exemplified as the ions contained in the positive electrode electrolytic solution, and titanium (Ti) ions are exemplified as the ions contained in the negative electrode electrolytic solution. In the case of an Mn—Ti-based electrolytic solution containing Mn ions as the positive electrode active material and Ti ions as the negative electrode active material, the positive electrode electrode 14 tends to be oxidatively deteriorated. Therefore, in the case of the Mn—Ti based electrolytic solution, if the electrode 100 is used for the positive electrode 14, the battery reactivity can be effectively enhanced for a long period of time.

The concentration of the positive electrode active material and the concentration of the negative electrode active material can be appropriately selected. For example, at least one of the concentration of the positive electrode active material and the concentration of the negative electrode active material is 0.3 mol / L or more and 5 mol / L or less. When the concentration is 0.3 mol / L or more, it can have an energy density (for example, about 10 kWh / m ³ ) that can be satisfactorily used as a large-capacity storage battery. The higher the concentration, the higher the energy density. Further, the above-mentioned concentration is 0.5 mol / L or more and 1.0 mol / L or more, and particularly 1.2 mol / L or more and 1.5 mol / L or more. When the above concentration is 5 mol / L or less, it is easy to increase the solubility in a solvent. It is easy to use the above concentration of 2 mol / L or less. An electrolytic solution satisfying this concentration is excellent in manufacturability.

Examples of the solvent of the electrolytic solution include an aqueous solution containing one or more acids or acid salts selected from the group consisting of sulfuric acid, phosphoric acid, nitric acid, and hydrochloric acid.

[Action effect]
The RF battery system 1 of this embodiment has excellent battery reactivity for a long period of time. The electrode 100 of the RF battery system 1 is composed of a composite oxide containing a first element that is difficult to dissolve in an electrolytic solution due to its acid resistance and a second element that contributes to improvement of battery reactivity in a specific ratio. This is because it has the catalyst 120 to be used.

<< Test Example 1 >>
An electrode on which a catalyst was supported on a substrate was prepared, and the composition of the catalyst provided on the electrode was investigated.

[Sample No. Sample No. 1-1 1-3]
The electrodes of each sample were produced through steps S1 to S3 similar to the above-described electrode manufacturing method.

The electrodes of each sample were prepared in the same manner in step S1 except that the ratios of the first salt and the second salt contained in the coating liquid were variously changed. A fiber aggregate was used as the material of the base material. The fibers constituting the fiber aggregate were carbon fibers. As the first salt, tin nitrate was used as the salt containing Sn. As the second salt, niobium ammonium oxalate was used as a salt containing Nb.

In step S2, the coating liquid was applied to the surface of the material by a dipping method. For drying after coating, the temperature was set to 150 ° C. and the time was set to 10 min.

In step S3, the heat treatment conditions were such that the atmosphere was an atmospheric atmosphere, the heat treatment temperature was 400 ° C., and the heat treatment time was 1 hour.

[Composition analysis]
The catalyst provided on the electrodes of each sample was X-ray diffracted with Cu Kα rays to examine the composition of the catalyst. For X-ray diffraction, Empyrean manufactured by Malvern Panalistical Co., Ltd. was used. The obtained spectrum is shown in FIG. The peak angle of a specific crystal plane extracted from the obtained spectrum is shown in FIG.

FIG. 10 is a graph showing the analysis results when the catalyst in each sample is X-ray diffracted. The vertical axis of FIG. 10 shows the intensity of the peak (Intensity [Normal]) converted so that the maximum value of the peak intensity of the catalyst in each sample is 1. The horizontal axis of FIG. 10 indicates the position of the peak (2θ [°]). The dotted line in FIG. 10 indicates the sample No. It is the analysis result of the catalyst in 1-1. The thick solid line in FIG. 10 indicates the sample No. It is the analysis result of the catalyst in 1-2. The broken line in FIG. 10 indicates the sample No. It is the analysis result of the catalyst in 1-3. The fine solid line in FIG. 10 is reference data and is X-ray diffraction data of SnO ₂ , which is a single oxide.

FIG. 11 is a graph showing the peak angle (°) of the (101) plane and the peak angle (°) of the (211) plane of the catalyst in each sample. The vertical axis on the left side of FIG. 11 shows the peak angle (°) of the (101) plane of the catalyst and the reference data of each sample. The vertical axis on the right side of FIG. 11 shows the peak angle (°) of the (211) plane of the catalyst and the reference data of each sample. The horizontal axis of FIG. 11 shows the ratio of the number of moles of Nb to the total number of moles of Sn and Nb contained in the catalyst in each sample. Each peak angle when the ratio of the number of moles of Nb on the horizontal axis is 0 means the peak angle of SnO ₂ which is the reference data. The solid line in FIG. 11 is the peak angle (°) of the (101) plane in each sample and reference data. The broken line in FIG. 11 is the peak angle (°) of the (211) plane in each sample and reference data.

As shown in FIG. 10, the position of the peak in each sample is deviated from the position of the peak in the reference data. As shown in FIG. 11, the peak angle (°) of the (101) plane and the peak angle (°) of the (211) plane in each sample are the peak angle (°) of the (101) plane and (°) in the reference data. 211) It is different for the peak angle (°) of the surface.

From these results, it was found that the catalyst in each sample was composed of a composite oxide of Nb and Sn, not a single oxide such as Nb ₂ O ₅ or SnO ₂ . Specifically, the sample No. The composition of the catalyst in 1-1 was found to be Nb _0.2 Sn _{0.8 OX} . Sample No. The composition of the catalyst in 1-2 was found to be Nb _0.4 Sn _{0.6 OX} . Sample No. The composition of the catalyst in 1-3 was found to be Nb _0.6 Sn _{0.4 OX} . In a composite oxide, the combination of the "elemental symbol" and the "subscript number immediately after the elemental symbol" means the ratio of the number of moles of the elemental symbol. This meaning is the same in Test Example 2 and Test Example 3 described later. For example, Nb _0.2 Sn _{0.8 OX} means that the ratio of the number of moles of Nb to the total number of moles of Nb and Sn is 0.2, and the ratio of the number of moles of Sn is 0.8. means. From this result, by changing the ratio of the first salt and the second salt contained in the coating liquid, a catalyst made of a composite oxide having a different ratio of the number of moles of the two elements is supported on the substrate. It was found that the electrode was obtained.

<< Test Example 2 >>
The difference in battery reactivity due to the difference in powder composition was investigated.

[Sample No. From 2-1 sample No. 2-13]
Sample No. 2-1 Sample No. 2-6, Sample No. 2-11 and sample No. The powder of 2-12 is composed of a single oxide. Sample No. From 2-2, sample No. 2-5, Sample No. From 2-7, sample No. 2-10 and sample No. The powder of 2-13 is composed of a composite oxide of a first element and a second element. The notation of the composite oxide is in the order of the second element, the first element, and O. For example, in the notation "NbSnO", Nb is the second element and Sn is the first element.

Sample No. The single oxide of 2-1 is SnO ₂ .
Sample No. The single oxide of 2-6 is Nb ₂ O ₅ .
Sample No. The single oxide of 2-11 is CeO ₂ .
Sample No. The single oxide of 2-12 is TiO ₂ .

Sample No. The composite oxide of 2-2 is Nb _0.1 Sn _{0.9 OX} .
Sample No. The composite oxide of 2-3 is Nb _0.2 Sn _{0.8 OX} .
Sample No. The composite oxide of 2-4 is Nb _0.4 Sn _{0.6 OX} .
Sample No. The composite oxide of 2-5 is Nb _0.6 Sn _{0.4 OX} .
Sample No. The composite oxide of 2-7 is Mn _0.2 Sn _{0.8 OX} .
Sample No. The composite oxide of 2-8 is Cu _0.2 Sn _{0.8 OX} .
Sample No. The composite oxide of 2-9 is Ce _0.2 Sn _{0.8 OX} .
Sample No. The composite oxide of 2-10 is Mn _0.8 Ce _{0.2 OX} .
Sample No. The composite oxide of 2-13 is Nb _0.6 Ti _{0.4 OX} .

[Battery reactivity]
An electrode made of a mixed material in which the powder of each sample and carbon paste were mixed was prepared, and linear sweep voltammetry measurement was performed using the electrode. Specifically, the electrodes of each of the prepared samples were immersed in a precharged electrolytic solution, and potential scanning was performed. The electrolytic solution contains manganese ions having a concentration of 1.0 mol / L. The potential scanning was performed at 3 mV / s from the open circuit voltage of the charged electrolytic solution to the low potential side using the silver / silver chloride electrode as a reference electrode. The results are shown in FIGS. 12 to 16.

The vertical axis of FIGS. 12 to 16 is the response current value. The horizontal axis of FIGS. 12 to 16 is the applied potential. In the linear sweep voltammogram shown in FIGS. 12 to 16, the larger the current value on the high potential side, the greater the battery reactivity on the electrode, that is, the powder contributes to the improvement of the battery reactivity.

In FIG. 12, the fine solid line is the sample No. As a result of 2-1 the broken line is the sample No. As a result of 2-2, the thick dashed line is the sample No. As a result of 2-3, the thick solid line is the sample No. As a result of 2-4, the dotted line is the sample No. The result of 2-5 is shown.
The solid line in FIG. 13 is the sample No. The result of 2-6 is shown.
In FIG. 14, the solid line is the sample No. As a result of 2-7, the broken line is the sample No. The result of 2-8 is shown.
In FIG. 15, the thick solid line indicates the sample No. As a result of 2-9, the alternate long and short dash line is the sample No. As a result of 2-10, the fine solid line is the sample No. The result of 2-11 is shown.
In FIG. 16, the fine solid line is the sample No. As a result of 2-12, the thick solid line is the sample No. The result of 2-13 is shown.

As shown in FIGS. 12 to 16, the sample No. From 2-3, sample No. 2-5, Sample No. From 2-7, sample No. 2-9 and sample No. It can be seen that in 2-13, the absolute value of the peak current value is large on the high potential side, specifically, when the potential is around 1.2 V. The reduction potential of Mn ³⁺ → Mn ²⁺ in the electrolytic solution is about 1.2 V. That is, the fact that the absolute value of the peak current value is large when the potential is around 1.2 V means that the battery reactivity is improved. It can be seen that these samples have a relatively small absolute value of the peak current value on the lower potential side than the reduction potential, for example, at 0.6 V or less. A small absolute value of the peak current value on the low potential side means that it is not dissolved in the electrolytic solution. In these samples, the absolute value of the peak current value on the low potential side is, for example, the sample No. Some samples are similar to 2-1. That is, among these samples, the sample No. Some samples are as difficult to dissolve in the electrolyte as 2-1.

From Test Example 2, the composite oxide of the specific first element and the specific second element satisfies the ratio of the number of moles of the first element to 0.4 or more and less than 0.9, and the ratio of the number of moles of the second element. It was found that when the value is more than 0.1 and 0.6 or less, it is easy to achieve both improvement of battery reactivity and extension of life.

<< Test Example 3 >>
An electrode on which the catalyst was supported was prepared, and the difference in cell resistivity and charge resistivity due to the presence or absence of the catalyst and the difference in the composition of the catalyst was investigated.

[Sample No. 3-1 Sample No. 3-2]
Sample No. The electrode of 3-1 is the sample No. It was produced in the same manner as 1-1.

Sample No. The electrode of 3-2 is the sample No. It was produced in the same manner as 1-3.

[Sample No. From 3-3, sample No. 3-6]
Sample No. From 3-3, sample No. The electrodes of 3-5 were sample No. 3 except that the types and proportions of the first salt and the second salt contained in the coating liquid were variously changed in step S1. It was produced in the same manner as 1-1.

(Sample No. 3-3)
As the first salt, titanium oxide sulfate was used as a salt containing Ti.
As the second salt, niobium ammonium oxalate was used as a salt containing Nb.

(Sample No. 3-4)
As the first salt, tin nitrate was used as a salt containing Sn.
As the second salt, cerium carbonate was used as a salt containing Ce.

(Sample No. 3-5)
As the first salt, tin nitrate was used as a salt containing Sn.
As the second salt, manganese nitrate was used as a salt containing Mn.

(Sample No. 3-6)
Sample No. For the electrodes of 3-6, sample No. 3-6 was prepared in step S1 except that a coating liquid containing only the first salt was prepared. It was produced in the same manner as 1-1.
As the first salt, cerium carbonate was used as a salt containing Ce.

[Sample No. 3-7]
Sample No. The electrodes of 3-7 consisted only of a base material without a catalyst. The substrate was composed of fiber aggregates. The fibers constituting the fiber aggregate were carbon fibers.

[Composition analysis]
Sample No. Sample No. from 3-1. The composition of the catalyst provided in the electrodes of 3-6 was described in Sample No. It was examined by X-ray diffraction in the same manner as 1-1. Sample No. Sample No. from 3-1. The catalyst of 3-5 was found to consist of a composite oxide. Sample No. The 3-6 catalyst was found to consist of a single oxide. Specifically, it was as follows.

Sample No. The catalyst of 3-1 was Nb _0.2 Sn _{0.8 OX} .
Sample No. The catalyst of 3-2 was Nb _0.6 Sn _{0.4 OX} .
Sample No. The catalyst of 3-3 was Nb _0.2 Ti _{0.8 OX} .
Sample No. The catalyst of 3-4 was Ce _0.2 Sn _{0.8 OX} .
Sample No. The catalyst of 3-5 was Mn _0.2 Sn _{0.8 OX} .
Sample No. _The catalyst for 3-6 was CeO2.

Sample No. Sample No. from 3-1. In 3-5, the abundance ratio of the catalyst composed of the composite oxide in the whole catalyst was 100% by mass. Sample No. In 3-6, the abundance ratio of the catalyst composed of a single oxide to the whole catalyst was 100% by mass.

[Cell resistivity]
A single cell battery was prepared using the electrodes of each sample, and the cell resistivity (Ω · cm ² ) was measured. The single cell battery was configured by arranging a positive electrode on one side of one diaphragm and a negative electrode on the other side, and sandwiching both sides of the electrode with a cell frame provided with a bipolar plate. The positive electrode has the above sample No. Sample No. from 3-1. The 3-7 electrode was used. For the negative electrode, sample No. The same electrodes as 3-7 were used. As the positive electrode electrolyte, a manganese sulfate solution containing manganese ions as an active material was used. As the negative electrode electrolyte, a titanium sulfate solution containing titanium ions as an active material was used.

The single cell battery of each sample was charged and discharged with a constant current having a current density of 100 mA / cm ² . In this test, multiple cycles of charging and discharging were performed. Specifically, in this test, when a preset predetermined switching voltage was reached, charging was switched to discharging, and when a preset predetermined switching voltage was reached, discharging was switched to charging. After charging and discharging, the cell resistivity was determined for each sample. The cell resistivity was calculated by {(difference between average voltage during charging and average voltage during discharging) / (average current / 2)} × effective cell area. The average voltage during charging and the average voltage during discharging were set to the average voltage in any one cycle among the plurality of cycles. In this test, the cell resistivity at the electrode immediately after the start of immersion in the electrolytic solution, specifically, the number of days of immersion was 0, was determined. The results are shown in Table 1.

[Charge transfer resistivity]
The electrolytic solution was supplied to the single cell battery of each sample, and the charge transfer resistivity (Ω · cm ² ) was measured by the AC impedance method. The charge transfer resistivity was measured by applying a bias around the open circuit voltage using a commercially available measuring device, and the voltage amplitude was 10 mV and the measurement frequency range was 10 kHz to 10 MHz. The results are shown in Table 1.

As shown in Table 1, the sample No. Sample No. from 3-1. The cell resistivity and charge transfer resistivity of 3-5 are the sample No. 3-6 and sample No. It can be seen that it is smaller than 3-7.

Sample No. Sample No. from 3-1. The cell resistivity of 3-5 is 2.00 Ω · cm ² or less. Among these samples, there are samples having a cell resistivity of 1.95 Ω · cm ² or less, further satisfying 1.85 Ω · cm ² or less, and particularly satisfying 1.80 Ω · cm ² or less. Sample No. Sample No. from 3-1. The cell resistivity of 3-5 is the sample No. Compared with 3-7, it decreased by 2% or more. In these samples, the cell resistivity is the sample No. There is a sample that is reduced by 3% or more, further reduced by 8% or more, and particularly reduced by 10% or more as compared with 3-7.

Sample No. Sample No. from 3-1. The charge transfer resistivity of 3-5 is 1.15 Ω · cm ² or less. Among these samples, there are samples having a charge transfer resistivity of 1.08 Ω · cm ² or less, further satisfying 1.03 Ω · cm ² or less, and particularly satisfying 1.00 Ω · cm ² or less. Sample No. Sample No. from 3-1. The charge transfer resistivity of 3-5 is the sample No. Compared with 3-7, it decreased by 8% or more. In these samples, the charge transfer resistivity is the sample No. There is a sample which is reduced by 10% or more, further reduced by 14% or more, and particularly reduced by 16% or more as compared with 3-7.

Sample No. Sample No. from 3-1. In the 3-5 electrode, a catalyst made of a composite oxide in which the ratio of the number of moles of the first element and the ratio of the number of moles of the second element satisfy a specific range is supported on the base material. On the other hand, sample No. 3-6 and sample No. The 3-7 electrode does not include a catalyst made of the above composite oxide. Therefore, the sample No. Sample No. from 3-1. The cell resistivity and electrolytic transfer resistivity of 3-5 are the sample No. 3-6 and sample No. It is considered that it was lower than 3-7.

The present invention is not limited to these examples, and is indicated by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

1 RF battery system 100 electrode 110 base material 111 fiber aggregate 111a fiber 112 sintered body 112a particle 120 catalyst 121 first catalyst 130 binder 10 battery cell 11 diaphragm 14 positive electrode 15 negative electrode electrode 16 cell frame 160 recess 161 bipolar plate 162 frame Body 163, 164 Liquid supply manifold 163s, 164s Liquid supply slit 165, 166 Drainage manifold 165s, 166s Drainage slit 167 Seal member 10P Positive electrode circulation mechanism 10N Negative electrode circulation mechanism 18 Positive electrode electrolyte tank 19 Negative electrode electrolyte tank 20, 21 Supply pipe 22, 23 Discharge pipe 24, 25 Pump 200 Cell stack 200s Substack 210 Supply / discharge plate 220 End plate 230 Tightening mechanism 500 AC / DC converter 510 Power generation unit 520 Substation equipment 530 Load

Claims (9)

An electrode comprising a base material and a catalyst supported on the base material.
The catalyst includes a first catalyst composed of a composite oxide of a first element and a second element.
The first element and the second element are different elements and are different from each other.
The first element is one element selected from the group consisting of Ti, Sn, Ce, W, Ta, Mo, and Nb.
The second element is one element selected from the group consisting of Nb, Mn, Fe, Cu, Ti, Sn, and Ce.
The ratio of the number of moles of the first element to the total number of moles of the first element and the second element in the composite oxide is 0.4 or more and less than 0.9.
electrode. The shape of the catalyst is the shape of at least one selected from the group consisting of a spherical shape, an ellipsoidal shape, a scaly shape, a needle shape, a polygonal columnar shape, a columnar shape, an elliptical columnar shape, a membrane shape, and a layered shape. Electrode. The electrode according to claim 1 or 2, wherein the material of the base material is C or Ti. The base material is a fiber aggregate or a sintered body, and is
The electrode according to any one of claims 1 to 3, wherein the fiber aggregate is a non-woven fabric, a woven fabric, or paper. The electrode according to any one of claims 1 to 4, comprising a binder in which the catalyst is bonded to the substrate. The electrode according to claim 5, wherein the binder contains at least one selected from the group consisting of resins, metals, carbides, and metal oxides. The electrode according to any one of claims 1 to 6 is provided.
Battery cell. The battery cell according to claim 7 is provided with a plurality of battery cells.
Cell stack. 1. The electrode according to any one of claims 1 to 6, the battery cell according to claim 7, or the cell stack according to claim 8 is provided.
Redox flow battery system.

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